The researchers from UK National Oceanographic Centre (NOC) also found that upper-middle income countries such as China would see the largest increase in flood costs, whereas the highest income countries would suffer the least, thanks to existing high levels of protection infrastructure.

The researchers from UK National Oceanographic Centre (NOC) also found that upper-middle income countries such as China would see the largest increase in flood costs, whereas the highest income countries would suffer the least, thanks to existing high levels of protection infrastructure.

"More than 600 million people live in low-elevation coastal areas, less than 10 metres above sea level. In a warming climate, global sea level will rise due to melting of land-based glaciers and ice sheets, and from the thermal expansion of ocean waters," said Svetlana Jevrejeva, from the NOC.

"So, sea level rise is one of the most damaging aspects of our warming climate," said Jevrejeva, lead author of the study published in the journal Environmental Research Letters.

Sea level projections exist for emissions scenarios and socio-economic scenarios. However, there are no scenarios covering limiting warming below the two degrees Celsius and 1.5 degree Celsius targets during the entire 21st century and beyond.

The study team explored the pace and consequences of global and regional sea level rise with restricted warming of 1.5 and 2 degrees Celsius, and compared them to sea level projections with unmitigated warming following emissions scenario Representative Concentration Pathway (RCP) 8.5.

Using World Bank income groups (high, upper middle, lower middle and low income countries), they then assessed the impact of sea level rise in coastal areas from a global perspective, and for some individual countries using the Dynamic Interactive Vulnerability Assessment modelling framework.

"We found that with a temperature rise trajectory of 1.5 degree Celsius, by 2100 the median sea level will have risen by 0.52 metres. But, if the 2 degree Celsius target is missed, we will see a median sea level rise of 0.86 metres, and a worst-case rise of 1.8 metres," Jevrejeva said.

"If warming is not mitigated and follows the RCP8.5 sea level rise projections, the global annual flood costs without adaptation will increase to USD 14 trillion per year for a median sea level rise of 0.86 metres, and up to USD 27 trillion per year for 1.8 metres. This would account for 2.8 per cent of global GDP in 2100," she said.

The projected difference in coastal sea levels is also likely to mean tropical areas will see extreme sea levels more often.

"These extreme sea levels will have a negative effect on the economies of developing coastal nations, and the habitability of low-lying coastlines," said Jevrejeva.

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